The defense against viral pathogens by human natural killer (NK) cells is a significant area of medical research because a deficiency in NK cells results in debilitating disease or even death due to herpesvirus infections by viruses such as human cytomegalovirus (HCMV). NK cells express a diverse repertoire of receptors killer immunoglobulin-like receptors (KIR), that are specific for major histocompatibility complex (MHC) class I. Preliminary data suggest a heterogeneous response among NK cell clones in their ability to detect and lyse HCMV infected cells, which undergo virally-mediated MHC class I downregulation. The objective of this four-year study is to determine the mechanisms of human NK cell recognition of HCMV infected cells. The hypothesis is that distinct subsets of NK cells, defined by their expression of particular KIR are responsible for the recognition of HCMV infected cells through their detection of decreased MHC class I expression. This will be tested through two specific aims: 1) to determine the role of inhibitory receptors in the detection of HCMV infection and 2) to determine the role of MHC class I expression in the detection of HCMV infection. The methods used in these approaches include: flow cytometry and sequence specific primer typing of receptor expression on NK clones, in vitro cell killing assays and the use of a mutant HCMV strain, RV798 that lacks the ability to downregulate class I expression. Unlike previous studies that use unnatural, allogeneic cells, only autologous infected skin fibroblasts will be used. Dr. Carr, the principal investigator, has an extensive interest in innate immunity, through his prior clinical experience as an aquatic veterinarian in shrimp aquaculture. Dr. Carr's long term goal of conducting research in cellular immunity is advanced through both the research/ training plan and the exceptional training environment at Stanford University, the performance site. The training plan supports the completion of Dr. Carr's Ph.D. training at Stanford and his transition to a postdoctoral fellow position at the University of California at San Francisco (UCSF). This plan builds upon Dr. Carr's previous experience through the acquisition of new research skills and expertise in molecular biology, human cell culture, cellular immunology, immunogenetics and herpesvirology. Stanford offers intensive training opportunities including weekly scientific seminars, retreats, journal clubs, and conferences. Furthermore, co-sponsors at Stanford, Drs. Peter Parham and Edward Mocarski, are renowned and accomplished researchers in the fields of immunogenetics and herpesvirology, respectively. Similarly, collaborations with Drs. Lewis Lanier at UCSF and Joe Phillips at DNAX, a biotechnology company, provide complementary expertise in NK cell biology and cellular immunology on this project. An objective of the training plan is that Dr. Carr will be competitive for a RO1 on cellular, innate immunity to be submitted by the end of the four-year award period.